A quota (which, it is to be remembered, is, in English, a noun in the singular) is an object of experience which seems to be a collection, although it may not be easy precisely to state what the determining description is.

The difference between a collection and a quota is, then, merely that a collection is an ens rationis, a creation of logic which retains its nature as a collection just the same whether it exists or not; while a quota is an object of experience whose existence is indubitable, and however perfect may be our assurance that it is a complete collection, yet it is not the fact that it really is so, but the fact that it appears to be so which makes it a quota.